If you have only used 1 to 3 times in a month, then for 10 to 30 days you most likely will test positive, if you are a heavy user (3 times a week) then up to 60 days:

There is nothing that you can take that will speed up the bodies removal of THC, how long it takes for you to become clean depends on how much you have used and the potency and on the way your body stores excess THC. The type and sensitivity of the test will also determine if you test clean or not. Drinking a lot of water or other fluids does not remove THC from your body, but may dilute its concentration in urine.

"Driving after smoking even a small amount of marijuana almost doubles the risk of a fatal highway accident, according to an extensive study of 10,748 drivers involved in fatal crashes between 2001 and 2003”. - http://alcoholism.about.com/od/pot/a/pot_driving.htm

Marijuana smoke was listed as a cancer-causing agent in California June 19, 2009
http://oehha.ca.gov/prop65/prop65_list/files/p65single072012.pdf

“Driving under the influence of cannabis was associated with a significantly increased risk of motor vehicle collisions” - http://www.bmj.com/content/344/bmj.e536

Even after adjusting the figures to take account of the other known risk factors, marijuana use remained a clear risk factor for testicular cancer. Just being a marijuana smoker seemed to carry a 70% extra risk, while those who smoked it regularly, or had smoked from an early age, had twice the risk compared to those who had never smoked it. - http://news.bbc.co.uk/2/hi/7869709.stm

Research now indicates that marijuana use increases the risk of depression, as well as schizophrenia. -http://www.health.harvard.edu/fhg/updates/update0503c.shtml

Britain's most senior coroner is warning that hundreds of young people are dying in accidents caused by their prolonged use of cannabis….The dangers of cannabis were highlighted in research published last month, which showed a sharp increase in drug-related deaths. According to the European Centre for Addiction Studies at St George's Hospital Medical School in London, in 2002, British coroners cited cannabis as the major cause of death in 18 out of 853 drug-related deaths. The drug was also implicated in a further 31 out of 1,579 deaths involving a cocktail of drugs. http://www.telegraph.co.uk/news/uknews/1445718/Cannabis-use-causes-hundreds-of-deaths-a-year-coroner-warns.html

""I have seen many cases of exacerbations of schizophrenia and bipolar disorder brought on by marijuana use," said psychiatrist Kenneth Certa, M.D., a member of the Section Council on Psychiatry. "Another problem I can see is that the marijuana in the community is often not very pure and is frequently adulterated with PCP [phencyclidine, an hallucinogen], which can also cause problems with psychosis." - http://psychnews.psychiatryonline.org/newsarticle.aspx?articleid=112336

Our results provide support that cannabis use plays an important role in the development of psychosis in vulnerable individuals. Cannabis use in early adolescence should be discouraged. - http://www.ncbi.nlm.nih.gov/pubmed/21883099
The risk to develop psychotic symptoms and also schizophrenic psychoses is thus explicitly elevated for young people who use cannabis. - http://www.ncbi.nlm.nih.gov/pubmed/19080993

“Chronic marijuana use has multiple adverse effects on the endocrine and reproductive systems. For example, chronic marijuana use is associated with reduced hypothalamic release of gonadotropin-releasing hormone, decreased plasma levels of gonadotropins (follicle-stimulating hormone, lutenizing hormone, and prolactin) and testosterone, reduced spermatogenesis, and impotency in men.” - http://onlinelibrary.wiley.com/doi/10.1002/cncr.24159/full